Transmitting/receiving filter device and communication device

ABSTRACT

First and second transmission paths P 1  and P 2  are disposed between a first port # 1  connected to an antenna ANT and a second port # 2  connected to a transceiving circuit  10 . The first transmission path P 1  includes receiving filters Rx 1 , Rx 2 , and Rx 2 ′, an amplification circuit LNA, and 90° hybrid circuits  12  and  14 . The second transmission path P 2  includes a transmitting filter Tx 1 . A received signal amplified by the amplification circuit LNA is transmitted to the port # 2  via the 90° hybrid circuits  12  and  14 , but is not transmitted to the second transmission path P 2 . A transmission signal is transmitted from the port # 2  to the second transmission path P 2 . This prevents oscillation of the received signal due to positive feedback. A transceiving filter device that prevents degradation in the insertion loss, noise figure, and group delay characteristics in the transmission frequency band or the receiving frequency band and that prevents oscillation, and a communication apparatus using the transceiving filter device are provided.

TECHNICAL FIELD

The present invention relates to a transceiving filter device thatselectively passes a transmission signal and a received signal, and to acommunication apparatus including the transceiving filter device.

BACKGROUND ART

In the related art, a base station in a mobile communication systemincludes a transceiving filter device having an amplification circuitbetween a tower antenna and a transceiving circuit for amplifying areceived signal.

For example, Patent Document 1 (International Publication No. 02/31997pamphlet) shows a transceiving filter device having first and secondtransmission paths between a first port connected to an antenna and asecond port connected to a transceiving circuit.

This structure is shown in FIG. 8. In FIG. 8, reference symbol ANTdenotes an antenna, reference numeral 10 denotes a transceiving circuit,reference numeral P1 denotes a first transmission path that allows areceived signal to pass, and reference numeral P2 denotes a secondtransmission path that allows a transmission signal to pass. The firsttransmission path P1 includes receiving filters Rx1 and Rx2 having abandpass characteristic that allows a received signal to pass, and anamplification circuit LNA. The second transmission path P2 includes atransmitting filter Tx1 having a bandstop characteristic that stops onlya received signal.

With this structure, a received signal input from the antenna ANT isamplified in the first transmission path P1, and is then sent to thetransceiving circuit 10, and a transmission signal from the transceivingcircuit 10 is sent to the antenna ANT via the second transmission pathP2.

However, as shown in FIG. 8, when the first and second transmissionpaths P1 and P2 are provided and either path includes an amplificationcircuit, the two transmission paths may form a feedback loop. Thetransmitting filter Tx1 passes the transmission frequency band and stopsthe receiving frequency band. However, if the amount of attenuation inthe vicinity of the receiving frequency band of the transmission filteris not satisfactory, the output signal of the amplification circuit LNAis oscillated because of positive feedback in the path ofRx2→Tx1→Rx1→LNA. In order to suppress occurrence of such oscillation, alarge amount of attenuation in the receiving frequency band of thetransmitting filter Tx1 must be maintained so that the loop gain isequal to or less than 1. Therefore, it is necessary to increase the stopbandwidth of the receiving frequency band of the transmitting filter Tx1or to reduce the pass bandwidths of the receiving filters Rx1 and Rx2.As a result, there arises a problem in that insertion loss (IL), nosefigure (NF), and group delay (GD) characteristics in the transmissionfrequency band or the receiving frequency band are degraded.

Accordingly, it is an object of the present invention to provide atransceiving filter device that suppresses degradation in the insertionloss, noise figure, and group delay characteristics in the transmissionfrequency band or the receiving frequency band and that preventsoscillation, and to provide a communication apparatus using thetransceiving filter device.

DISCLOSURE OF INVENTION

In order to achieve the above-described object, the present inventionprovides a transceiving filter device including a first transmissionpath and a second transmission path between a first port connected to anantenna and a second port connected to a transceiving circuit, the firsttransmission path including an amplification circuit that amplifies areceived signal and a receiving filter that allows areceiving-frequency-band signal to pass, the second transmission pathallowing a transmission signal to pass, wherein an element that preventspositive feedback of the received signal in a loop formed of the firsttransmission path and the second transmission path is disposed in theloop.

With the element that prevents positive feedback of the received signal,positive feedback in which the received signal returns to the input sideof the first transmission path via the second transmission path does notoccur, thus preventing oscillation.

In the present invention, furthermore, the second transmission pathincludes a transmitting filter that passes the transmission signal andthat stops a receiving-frequency-band signal, and a circuit havingdirectivity in which the received signal amplified by the amplificationcircuit is transmitted to the second port and the transmission signalinput from the second port is transmitted to the second transmissionpath is disposed at the output side of the amplification circuit of thefirst transmission path and at a connection between the firsttransmission path and the second transmission path, wherein this circuitserves as the element that prevents positive feedback.

With this structure, the received signal passing through the firsttransmission path is transmitted to the second port, and is nottransmitted to the second transmission path. Positive feedback of thereceived signal does not occur, thus preventing oscillation.

In the present invention, furthermore, the circuit having directivity isformed of a coupled-line directional coupler that transmits the receivedsignal amplified by the amplification circuit to the second port andthat transmits the transmission signal input from the second port to thesecond transmission path, and a termination resistor that terminates aportion of the amplified received signal.

In the present invention, furthermore, the circuit having directivity isformed of a 90° hybrid circuit that transmits the received signalamplified by the amplification circuit to the second port and thattransmits the transmission signal input from the second port to thesecond transmission path, and a termination resistor that terminates aportion of the amplified received signal.

In the present invention, furthermore, the 90° hybrid circuit has aplurality of stages.

In the present invention, furthermore, the circuit having directivity isformed of a circulator that transmits the received signal amplified bythe amplification circuit to the second port and that transmits thetransmission signal input from the second port to the secondtransmission path.

The present invention further provides a communication apparatusincluding a duplexer antenna and a transceiving circuit, wherein thetransceiving filter device is disposed between the antenna and thetransceiving circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the structure of a communicationapparatus having a transceiving filter device according to a firstembodiment.

FIG. 2 is a block diagram showing the structure of a communicationapparatus having a transceiving filter device according to a secondembodiment.

FIG. 3 is a diagram showing the structure of hybrid circuits included inthe transceiving filter device.

FIG. 4 is a block diagram showing the structure of a communicationapparatus having a transceiving filter device according to a thirdembodiment.

FIG. 5 is a diagram showing the structure of a hybrid circuit includedin the transceiving filter device.

FIG. 6 is a characteristic chart of the hybrid circuit.

FIG. 7 is a block diagram showing the structure of a communicationapparatus having a transceiving filter device according to a fourthembodiment.

FIG. 8 is a block diagram showing the structure of a communicationapparatus having a transceiving filter device of the related art.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows the structure of a communication apparatus having atransceiving filter device according to a first embodiment. In FIG. 1,reference symbol ANT denotes an antenna of a base station, and atransceiving circuit 10 is a circuit that transmits and receives acommunication signal in the base station. In FIG. 1, the componentsother than the antenna ANT and the transceiving circuit 10 form atransceiving filter device 100.

The antenna ANT is connected to a first port #1 of the transceivingfilter device 100, and the transceiving circuit 10 is connected to asecond port #2 of the transceiving filter device 100. The transceivingfilter device 100 and the antenna ANT are disposed on the tower topportion of the base station. Reference numerals Rx1 and Rx2 denotereceiving filters having a bandpass characteristic that allows areceiving-frequency-band signal to pass and that stops atransmission-frequency-band signal. Reference symbol LNA denotes alow-noise amplification circuit. The two receiving filters Rx1 and Rx2are disposed on the input and output sides of the amplification circuitLNA, respectively, and these components are placed in a firsttransmission path P1.

Reference numeral Tx1 denotes a transmitting filter having a bandstopfilter characteristic that allows a transmission-frequency-band signalto pass and that stops a receiving-frequency-band signal. Thetransmitting filter Tx1 is placed in a second transmission path P2.

Reference numeral 11 denotes a coupled-line directional coupler. Thedirectional coupler 11 couples a line between ports (1) and (3) thereofand a line between ports (2) and (4) thereof, and separates the ports(1) and (4) and the ports (3) and (2). The ports (2) and (4) of thedirectional coupler 11 are connected to the second port #2 and thetransmitting filter Tx1, respectively. The port (1) is connected to thereceiving filter Rx2. The port (3) terminates with a resistor R.

Thus, an input signal from the port (1) of the directional coupler 11 isoutput to the ports (2) and (3). An input signal from the port (2) isoutput to the port (4). Therefore, a received signal from the antennaANT passes through the receiving filter Rx1, and is then amplified bythe amplification circuit LNA. The amplified signal passes through thereceiving filter Rx2, and is then output to the second port #2 via thedirectional coupler 11. A transmission signal from the transceivingcircuit 10 is input from the second port #2, passing through thetransmitting filter Tx1 via the directional coupler 11, and is thenoutput to the antenna ANT from the first port #1. The received signaloutput from the receiving filter Rx2 does not return to the secondtransmission path P2, and is not oscillated since positive feedback doesnot occur. Therefore, it is not necessary to forcedly increase the stopbandwidth of the receiving frequency band of the transmitting filter Tx1or to reduce the pass bandwidths of the receiving filters Rx1 and Rx2more than necessary. Moreover, the insertion loss, noise figure, andgroup delay characteristics of the transmission signal or receivedsignal are not degraded.

FIG. 2 shows the structure of a communication apparatus having atransceiving filter device according to a second embodiment. In thisexample, 90° hybrid circuits 12 and 13 and receiving filters Rx2 andRx2′ are disposed at the connection between the first transmission pathP1 and the second transmission path P2.

The 90° hybrid circuits (hereinafter referred to simply as “hybridcircuits”) 12 and 13 are power-halving circuits having directivity inthe signal transmission direction. The hybrid circuit 12 power-halvesthe received signal amplified by the amplification circuit LNA, and thehybrid circuit 13 outputs the received signal which has passed throughthe receiving filters Rx2 and Rx2′ to the port #2. As described below,the received signal which has passed through the receiving filters Rx2and Rx2′ is not transmitted to the second transmission path P2.

The receiving filters Rx2 and Rx2′ disposed between the two 90° hybridcircuits 12 and 13 pass the receiving frequency band and stop thetransmission frequency band. This prevents a transmission signal fromentering the first transmission path P1 from the port #2. The structureof the other components is similar to that of the first embodiment.

FIG. 3 shows the operation of the hybrid circuits 12 and 13. The linesat the four sides of each of the hybrid circuits 12 and 13 arerepresented by La, Lb, Lc, and Ld. Where the impedance of the lines Lcand Ld is Zo, the impedance of the lines La and Lb is given by Zo/√2.Each line has an electrical length of one-quarter the wavelength of thetransmission frequency. Therefore, the received signal input to thehybrid circuit 12 is power-halved into two opposite-phase signals, whichare then input to the receiving filters Rx2 and Rx2′, respectively. Thetwo receiving filters Rx2 and Rx2′ have substantially the same filtercharacteristic. The signals which have passed through the receivingfilters Rx2 and Rx2′ are phase-combined again by the hybrid circuit 13,and the result is transmitted to the port #2. The signals which are tobe transmitted in the direction indicated by a broken line shown in FIG.3 are combined in opposite phase, and are cancelled, so as not to betransmitted. The receiving filters Rx2 and Rx2′ inserted between the twohybrid circuits 12 and 13 allow received signals, once branched, to besuperposed in phase in the direction of the port #2 and to be superposedin opposite phase in the direction of the port #1 when they are combinedagain.

The transmission signal input from the port #2 is input to the receivingfilters Rx2 and Rx2′ via the hybrid circuit 13, but this signal isstopped by the receiving filters Rx2 and Rx2′ and is not input to theoutput side of the amplification circuit LNA shown in FIG. 2. Therefore,the amplification circuit LNA is not damaged and does not suffer fromdistortion such as intermodulation distortion.

In this way, the received signal is transmitted with directivity to theport #2, resulting in no positive feedback of the received signal by theloop of the two transmission paths P1 and P2 shown in FIG. 2.

The structure of a communication apparatus having a transceiving filterdevice according to a third embodiment will now be described withreference to FIGS. 4 through 6.

FIG. 4 is a block diagram of the transceiving filter device. The basicstructure of this transceiving filter device is the same as that of thetransceiving filter device shown in FIG. 2. In this example, one of two90° hybrid circuits, that is, a 90° hybrid circuit 14, has a two-stagestructure. The structure of the remaining components is similar to thatshown in FIG. 2.

FIG. 5 shows the structure of the hybrid circuit 14 portion. Each oflines L1 through L7 has an electrical length of one-quarter thewavelength of the transmission frequency. The impedances of these linesare as follows:

L1 through L4: 35.95 Ω

L5 and L6: 105.23 Ω

L7: 47.26 Ω

FIG. 6 shows characteristics of the two-stage hybrid circuit, in whichthe y-axis designates the transmission loss or the reflection loss,expressed in dB. The center frequency of the receiving frequency band is1950 MHz, and the transmission frequency band is outside the range of1920 MHz to 1980 MHz. In FIG. 6, the curve indicated by circlesrepresents the transmission characteristic (S21 characteristic) in thedirection of ports (1)→(2), the curve indicated by rectangles representsthe transmission characteristic (S32 characteristic) in the direction ofports (2)→(3) of the hybrid circuit, the curve indicated bydownward-pointing triangles represents the transmission characteristic(S31 characteristic) in the (1)→(3) direction, and the curve indicatedby upward-pointing triangles represents the reflection characteristic(S11 characteristic) of the port (1).

With such a two-stage 90° hybrid circuit, the S32 characteristicmaintains substantially 0 dB across a broad frequency band including thetransmission frequency band, thus achieving a low insertion losscharacteristic. Therefore, the transmission signal is transmitted fromthe port (2) to the port (3) with low losses. The S21 characteristicalso exhibits substantially 0 dB in the receiving frequency band, thusachieving a low insertion loss characteristic. Therefore, the receivedsignal is transmitted from the port (1) to the port (2) with low losses.

With the use of such a 90° hybrid circuit, therefore, the pass bandwidthof the transmission frequency band can increase. A 90° hybrid circuitwith three or more stages may also be used.

FIG. 7 shows the structure of a communication apparatus having atransceiving filter device according to a fourth embodiment. In thisexample, a circulator 15 is disposed at the connection between the firsttransmission path P1 and the second transmission path P2. The circulator15 is a circulator with a forward direction in the direction of ports(1)→(2) and (2)→(3). The received signal passing through thetransmission path P1 is input to the port (1) of the circulator 15, andis transmitted to the port #2 from the port (2). The transmission signalinput from the port #2 to the port (2) of the circulator 15 is outputfrom the port (3), and is transmitted to the second transmission pathP2.

Such a 2-GHz-band circulator can be manufactured at low cost, and thecost of the overall transceiving filter device can be reduced.

According to the present invention, in a transceiving filter deviceincluding a first transmission path and a second transmission pathbetween a first port connected to an antenna and a second port connectedto a transceiving circuit, the first transmission path including anamplification circuit that amplifies a received signal and a receivingfilter that allows a receiving-frequency-band signal to pass, the secondtransmission path allowing a transmission signal to pass, positivefeedback in which the received signal returns to the input side of thefirst transmission path via the second transmission path does not occur,thus preventing oscillation. Therefore, it is not necessary to increasethe stop bandwidth (receiving frequency bandwidth) of the transmittingfilter in the second transmission path or to reduce the pass bandwidthof the first transmission path for the received signal. As a result, theinsertion loss, noise figure, and group delay characteristics of thetransmission signal or the received signal can be improved.

According to the present invention, furthermore, a circuit havingdirectivity in which the received signal amplified by the amplificationcircuit is transmitted to the second port and the transmission signalinput from the second port is transmitted to the second transmissionpath is disposed at the output side of the amplification circuit of thefirst transmission path and at a connection between the firsttransmission path and the second transmission path. Therefore, thereceived signal passing through the first transmission path istransmitted to the second port, and is not transmitted to the secondtransmission path. Positive feedback of the received signal does notoccur, thus ensuring that oscillation is prevented.

According to the present invention, furthermore, the circuit havingdirectivity is formed of a coupled-line directional coupler and atermination resistor, thus preventing oscillation with the simplecircuit structure.

According to the present invention, furthermore, the circuit havingdirectivity is formed of a 90° hybrid circuit and a terminationresistor, thus preventing oscillation with the simple circuit structure.

According to the present invention, furthermore, the 90° hybrid circuithas a plurality of stages, thus increasing the pass bandwidth for thetransmission signal.

According to the present invention, furthermore, the circuit havingdirectivity is formed of a circulator, thus reducing the cost.

According to the present invention, furthermore, the transceiving filterdevice is disposed between a duplexer antenna and a transceivingcircuit, thus improving the insertion loss, noise figure, and groupdelay characteristics of the transmission signal or received signal.Therefore, a high-communication-performance communication apparatuscapable of high-speed transmission with a low data error rate can berealized.

INDUSTRIAL APPLICABILITY

As described above, a transceiving filter device according to thepresent invention provides improvement in insertion loss, noise figure,and group delay characteristics of a transmission signal or receivedsignal, and is suitable for a communication apparatus for use in, forexample, microwave-band or millimeter-wave-band radio communication orelectromagnetic wave transmission and reception.

1. A transceiving filter device comprising: a first transmission pathand a second transmission path between a first port for connection to anantenna and a second port for connection to a transceiving circuit, thefirst transmission path including: an amplification circuit thatamplifies a received signal; a receiving filter disposed at an inputside of the amplification circuit that allows a receiving-frequency-bandsignal to pass and stops a transmission signal; and a circuit havingdirectivity disposed at an output side of the amplification circuit; thesecond transmission path including a transmitting filter that allows thetransmission signal to pass and that stops the receiving-frequency-bandsignal, and wherein the circuit having directivity transmits thereceived signal amplified by the amplification circuit to the secondport and transmits the transmission signal input from the second port tothe second transmission path, the circuit having directivity including:at least two 90° hybrid circuits; two band pass filters having similarcharacteristics to each other and that pass thereceiving-frequency-band-signal and stop the transmission signal; and atermination resistor that terminates a portion of the received signalamplified by the amplification circuit, wherein output ports of the twoband pass filters are connected in parallel to a first 90° hybridcircuit of the at least two 90° hybrid circuits, and input ports of thetwo band pass filters are connected in parallel to a second 90° hybridcircuit of the at least two 90° hybrid circuits.
 2. The transceivingfilter device according to claim 1, wherein the at least two 90° hybridcircuits have a plurality of stages.
 3. A communication apparatuscomprising an antenna connected to the first port of the transceivingfilter device according to claim 1, and a transceiving circuit connectedto the second port of the transceiving filter device.
 4. A communicationapparatus comprising an antenna connected to the first port of thetransceiving filter device according to claims 2, and a transceivingcircuit connected to the second port of the transceiving filter device.